“Is she coming or what?”
You and your friend were supposed to meet someone at 8:00 for dinner, but she's 20 minutes late already. Your friend called her and they talked for a couple minutes. You ask this after your friend hangs up the phone.
Is she coming or what?
You can talk about the future with " be ___ing". For example:
Are you going?
I'm staying here.
Casey is running a half marathon next month.
When someone has already decided on a future action, it's more natural to use this than "will".
Use this phrase at the end of a yes/no question when you're a little annoyed and you want an immediate answer. For example, when you're shopping with someone who's taking a long time to decide, you ask:
Are you going to buy it or what?
In the example at top, the speaker is annoyed that the woman is late, so he asks "Is she coming or what?" This sentence expresses the idea that he doesn't want to wait for her much longer.
"...or what?" isn't used in written English.